Study finds decline in dolphins around Cornish coast

The number of bottlenose dolphins around Cornwall’s coast could be declining according to a new study by the University of Exeter and Cornwall Wildlife Trust.

Sightings and strandings of dolphins, porpoises and whales, collectively known as cetaceans, from around the Cornish coast have been collected and recorded by Cornwall Wildlife Trust for many years.

This data formed the basis of the research project between the Trust and the University of Exeter.

Stephen Pikesley, an MSc Biosciences student from the University of Exeter’s Cornwall Campus, has analysed the long term datasets on cetacean sightings and strandings off the coast of Cornwall. He has identified whether changes had occurred in the number of sightings and strandings since the early 1990s. 18 species were recorded sighted and/or stranded, with the most frequently seen being bottlenose dolphins, harbour porpoises, common dolphins, Risso’s dolphins and minke whales.

The study showed that the average size of bottlenose dolphin groups had halved during the study period, and the relative proportion of harbour porpoises and minke whales sighted around the Cornish coast had increased.

Stephen Pikesley, University of Exeter student said: “When we analysed these data it was clear that there were significant decreases in the number of bottlenose dolphin sightings between 1991 and 2008. We also found that the size of bottlenose dolphin groups had decreased. There was an increase in harbour porpoise and minke whale sightings, however, this should not necessarily be interpreted as a population increase but could indicate a shift in their distribution. Cetacean strandings, in general, have decreased over time although the picture is somewhat different for harbour porpoises, where strandings have increased”.

Ruth Williams, Marine Conservation Manager for Cornwall Wildlife Trust said: “The analyses that Stephen has carried out on the data collected by members of the public and our volunteers have provided great insight.